Forced air heating and cooling systems for indoor spaces in residential and commercial buildings are ubiquitous. A long-standing practice in controlling forced airflow through the heat exchanger, heating coils, evaporator coils and other heat exchange equipment in indoor space heating and cooling systems includes providing controls for the forced air fan or blower drive motor which delay startup of the drive motor when the heating or cooling source has been energized and another delay in shutdown of the fan drive motor after the heating/cooling system has been de-energized. Some conventional prior art controls do not provide for any delay of motor startup or shutdown. Conventional controls often provide for delayed startup of the fan drive motor at a single operating speed and delayed shutdown of the drive motor, again at a single maximum operating speed, after shutdown of the heating/cooling system in an effort to minimize unpleasant cold or hot drafts of air and to capture residual heat/cooling effect. However, controlling motor speed from being de-energized to full speed does not preclude stratification of air in the system ductwork or in the space being heated or cooled, nor does such operation maximize the capture of residual heat/cooling effect of the system heat exchange equipment.
Controls have also been developed for forced air heating/cooling systems wherein the indoor space air circulating fan drive motor is driven at reduced speed for a period of time during startup of the heating/cooling system and at a reduced speed for a period of time during the run-on or shutdown phase of the heating/cooling system operating cycle. Again, however, this type of control does not minimize the stratification of warm and cold air in the duct work or the space being heated or cooled nor does this type of system maximize the capture of residual heating/cooling effect.
Accordingly, there has been a strongly felt need for improvements in forced air circulation control in conventional heating and/or cooling systems including systems which use conventional electric motors, such as permanent split capacitor (PSC), shaded pole or other conventional electric motors used in a substantial number of heating/cooling systems manufactured for residential as well as commercial heating and cooling applications of indoor spaces. There has also been a strongly felt need for a fan or blower drive motor control system which may be easily retrofitted to a conventional heating/cooling system control circuits without modifying the circuits and without causing the controls for the heating/cooling system to be out of compliance with regulatory requirements. It is to these ends that the present invention has been developed.